Systems and methods for adaptive planning and control of a surgical tool

ABSTRACT

A surgical system includes a robotic device having a surgical tool, a tracking system, and a processing system communicably coupled to the robotic device. The processing system is configured to store a surgical plan comprising a first planned cut and one or more additional planned cuts, each additional cut defined by a relative angle and distance from the first planned cut, receive tracking data from the tracking system while the surgical tool makes a cut substantially corresponding to the first planned cut, and determine a recorded first cut plane based on the first tracking data. The processing system is further configured to determine an error between the recorded first cut plane and the planned first cut, the error comprising a deviation from the planned first cut, and update the surgical plan by modifying the one or more additional planned cuts based on the deviation.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of and priority to U.S. ProvisionalPatent Application No. 62/679,185, filed Jun. 1, 2018, which is herebyincorporated by reference in its entirety.

BACKGROUND

The present disclosure relates generally to surgical systems fororthopedic surgeries, and more particularly to surgical systems fortotal knee arthroplasty procedures. Total knee arthroplasty,colloquially referred to as knee replacement, is widely used to treatknee osteoarthritis and other damage to a patient's knee joint byreplacing portions of the knee anatomy with prosthetic components. In atotal knee arthroplasty procedure, for example, a patient's femur istypically modified to be joined to a prosthesis using a series of planarcuts to prepare the surface of the bone. The relative angle and distancebetween the cuts is crucial for effectively coupling the prosthesis tothe patient's femur and the overall success of the procedure.

One possible tool for use in total knee arthroplasty procedure is arobotically-assisted surgical system. A robotically-assisted surgicalsystem typically includes a robotic device that is used to prepare apatient's anatomy, such as by making bone cuts, a tracking systemconfigured to monitor the location of the robotic device relative to thepatient's anatomy, and a computing system configured to monitor andcontrol the robotic device. Robotically-assisted surgical systems, invarious forms, autonomously carry out surgical tasks, provide forcefeedback to a user manipulating a surgical device to complete surgicaltasks, augment surgeon dexterity and precision, and/or provide othernavigational cues to facilitate safe and accurate surgical operations.

A surgical plan is typically established prior to performing a surgicalprocedure with a robotically-assisted surgical system. The surgical planmay be patient-specific. Based on the surgical plan, the surgical systemguides, controls, or limits movements of the surgical tool duringportions of the surgical procedure. Guidance and/or control of thesurgical tool serves to protect the patient and to assist the surgeonduring implementation of the surgical plan. In a total knee arthroplastyoperation, a robotically-assisted surgical system can be used to helpcarry out a surgical plan that includes making the necessary planar cutsmentioned above, for example by providing force feedback to guide acutting tool to make the pre-planned planar cuts under surgeon control.

Each actual cut may result in some amount of error in the actualposition and orientation of the cut relative to the planned cut. Forexample, error may be caused by technical limitations of surgical toolsincluding robotic devices, limitations on surgeon dexterity, perception,skill, and/or surgeon mistakes. When multiple cuts, each with its ownerror, are made according to a pre-established plan, the errors forindividual cuts often compound to cause substantial relative errorsbetween cuts, for example increasing an angle between adjacent cuts ordecreasing the distance between two cuts. These relative cutting errorsmay lead to the need for harmful and time-consuming corrective cuts,difficulty in coupling a prosthetic component to the patient's femur,misaligned prosthetic components, and other surgical complications.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A is a first perspective view of a portion of a femur as preparedin a total knee arthroplasty procedure, according to an exemplaryembodiment.

FIG. 1B is a second perspective view of a portion of a femur as preparedin a total knee arthroplasty procedure, according to an exemplaryembodiment.

FIG. 2 is an illustration of a surgical system, according to anexemplary embodiment.

FIG. 3 is a flowchart of a process for minimizing relative cuttingerrors in a total knee arthroplasty procedure, according to an exemplaryembodiment.

FIG. 4 is a flowchart of another process for minimizing cutting error ina total knee arthroplasty procedure, according to an exemplaryembodiment.

FIGS. 5A-C are visualizations of planned surgical cuts for use in theprocess of FIG. 4, according to an exemplary embodiment.

FIG. 6 is a cross-sectional view of the planned surgical cuts of FIGS.5A-C as in the process of FIG. 4, according to an exemplary embodiment.

FIGS. 7A-B are cross-sectional views of the planned surgical cuts ofFIGS. 5A-6 with a recorded distal cut plane and the planned cuts of afirst updated surgical plan as in the process of FIG. 4, according to anexemplary embodiment.

FIGS. 8A-B are cross-sectional views of the surgical plans of FIGS.5A-7B with a recorded posterior cut plane and the planned cuts of asecond updated surgical plan as in the process of FIG. 4, according toan exemplary embodiment.

FIGS. 9A-B are cross-sectional views of the surgical plans of FIGS.5A-8B with a recorded anterior cut plane and the planned cuts of a thirdupdated surgical plan as in the process of FIG. 4, according to anexemplary embodiment.

FIG. 10 is a cross-sectional view of the planned surgical cuts of FIGS.5A-6 with a visualization of the final completed cuts, according to anexemplary embodiment.

DETAILED DESCRIPTION

Referring to FIGS. 1A-1B, a portion of a femur 100 prepared to receive aprosthetic component in a total knee arthroplasty procedure is shown.The portion of the femur 100 shown in FIGS. 1A-1B is the distal end ofthe femur, i.e., the portion that interacts with the tibia in the kneejoint. The femur 100 has been modified by five substantially planar cutsto create five substantially planar surfaces, namely distal surface 102,posterior chamfer surface 104, posterior surface 106, anterior surface108, and anterior chamfer surface 110. The anterior surface 108 sharesan edge 112 with anterior chamfer surface 110, which shares an edge 114with distal surface 102, which shares an edge 116 with posterior chamfersurface 104, which shares an edge 118 with posterior surface 106. Thecreation of five planar cuts as shown in FIGS. 1A-1B and describedelsewhere herein are provided as an example only, and any number ofplanar cuts may be planned and modified in the same fashion describedherein. Furthermore, the same and similar aspects described herein canbe similarly applied to preparation of any bone of a joint.

The surfaces 102-110 can be defined by their angles and positionsrelative to one another and to the femur 100, for example as defined bya reference coordinate system. When oriented and positioned as in FIGS.1A-B, precise relative orientation and positioning allows surfaces102-110 to be abutted flush against a femoral component (not shown) of aknee prosthesis with a matching geometrical structure (e.g., with a setof surfaces oriented and shaped like surfaces 102-110). In such a case,the femoral component is then also properly aligned with the femur 100,other prosthetic components, and other anatomical features to providepositive surgical outcomes for a patient (e.g., short recovery times,full range of motion, pain-free mobility, long-term reliability).

However, because of technical limitations and bounds on surgeonperception and dexterity and/or on available surgical tools, some amountof error in the cuts that create the surfaces 102-110 is common. Errorin the relative position or angle of the surfaces 102-110 may preventthe femur from properly engaging a prosthetic device. Because eachsurface 102-110 is connected to another surface 102-110 along at leastone edge 112-118, an error in the orientation or position of one surfaceis likely to cause a distortion in one or more neighboring surfaces. Forexample, if the distal surface 102 is shifted to be oriented at agreater angle relative to the anterior chamfer surface 110, a distanceand angle between the distal surface 102 and the posterior chamfersurface 104 may also be distorted. The overall shape created by thesurfaces 102-110, then, is also distorted. In such a case, the femoralcomponent of a prosthetic device may not align properly with surfaces102-110, potentially causing negative surgical outcomes, the need forfollow up procedures, and limited mobility and/or chronic pain for thepatient. Thus, a need exists for surgical systems and methods forminimizing the relative cutting error between the five femoral cuts. Asdescribed herein, intraoperative updates to a surgical plan for use witha robotically-assisted surgical system can help to minimize relativecutting errors of, for example, femoral cuts of a total kneearthroplasty procedure.

Referring now to FIG. 2, a surgical system 200 for orthopedic surgery isshown, according to an exemplary embodiment. In general, the surgicalsystem 200 is configured to facilitate the planning, cutting, and errorminimization of cuts required to form surfaces 102-110 of FIG. 1. Asshown in FIG. 2, the surgical system 200 is set up to treat a leg 202 ofa patient 204 sitting or lying on table 205. Leg 202 includes femur 206and tibia 208, between which a prosthetic knee implant is to beimplanted in a total knee arthroscopy procedure. To facilitate theprocedure, surgical system 200 includes robotic device 220, trackingsystem 222, and computing system 224.

The robotic device 220 is configured to modify a patient's anatomy(e.g., femur 206 of patient 204) under the control of the computingsystem 224. One embodiment of the robotic device 220 is a haptic device.“Haptic” refers to a sense of touch, and the field of haptics relatesto, among other things, human interactive devices that provide feedbackto an operator. Feedback may include tactile sensations such as, forexample, vibration. Feedback may also include providing force to a user,such as a positive force or a resistance to movement. One use of hapticsis to provide a user of the device with guidance or limits formanipulation of that device. For example, a haptic device may be coupledto a surgical tool, which can be manipulated by a surgeon to perform asurgical procedure. The surgeon's manipulation of the surgical tool canbe guided or limited through the use of haptics to provide feedback tothe surgeon during manipulation of the surgical tool.

Another embodiment of the robotic device 220 is an autonomous orsemi-autonomous robot. “Autonomous” refers to a robotic device's abilityto act independently or semi-independently of human control by gatheringinformation about its situation, determining a course of action, andautomatically carrying out that course of action. For example, in suchan embodiment, the robotic device 220, in communication with thetracking system 222 and the computing system 222, may autonomouslycomplete the series of femoral cuts mentioned above without direct humanintervention.

The robotic device 220 includes a base 230, a robotic arm 232, and asurgical tool 234, and is communicably coupled to the computing system224 and the tracking system 222. The base 230 provides a moveablefoundation for the robotic arm 232, allowing the robotic arm 232 and thesurgical tool 234 to be repositioned as needed relative to the patient204 and the table 205. The base 230 may also contain power systems,computing elements, motors, and other electronic or mechanical systemnecessary for the functions of the robotic arm 232 and the surgical tool234 described below.

The robotic arm 232 is configured to support the surgical tool 234 andprovide a force as instructed by the computing system 224. In someembodiments, the robotic arm 232 allows a user to manipulate thesurgical tool and provides force feedback to the user. In such anembodiment, the robotic arm 232 includes joints 236 and mount 238 thatinclude motors, actuators, or other mechanisms configured to allow auser to freely translate and rotate the robotic arm 232 and surgicaltool 234 through allowable poses while providing force feedback toconstrain or prevent some movements of the robotic arm 232 and surgicaltool 234 as instructed by computing system 224. As described in detailbelow, the robotic arm 232 thereby allows a surgeon to have full controlover the surgical tool 234 within a control object while providing forcefeedback along a boundary of that object (e.g., a vibration, a forcepreventing or resisting penetration of the boundary). In someembodiments, the robotic arm is configured to move the surgical tool toa new pose automatically without direct user manipulation, as instructedby computing system 224, in order to position the robotic arm as neededand/or complete certain surgical tasks, including, for example, cuts ina femur 206.

The surgical tool 234 is configured to cut, grind, drill, partiallyresect, reshape, and/or otherwise modify a bone. More particularly, forpreparation of a distal femur having five planar cuts, surgical tool 234is configured to make a distal cut, a posterior chamfer cut, a posteriorcut, an anterior cut, and an anterior chamfer cut in femur 206 to createthe distal surface 102, posterior chamfer surface 104, posterior surface106, anterior surface 108, and anterior chamfer surface 110 as shown inFIG. 1 (i.e., to reshape femur 206 like femur 100). The surgical tool234 may be any suitable tool, and may be one of multiple toolsinterchangeably connectable to robotic device 220. For example, as shownin FIG. 2 the surgical tool 234 is a spherical burr. The surgical toolmay also be a sagittal saw, for example with a blade aligned parallelwith a tool axis or perpendicular to the tool axis.

Tracking system 222 is configured track the patient's anatomy (e.g.,femur 206 and tibia 208) and the robotic device 220 (i.e., surgical tool234 and/or robotic arm 232) to enable control of the surgical tool 234coupled to the robotic arm 232, to determine a position and orientationof cuts made by the surgical tool 234, and allow a user to visualize thefemur 206, the tibia 208, the surgical tool 234, and/or the robotic arm232 on a display of the computing system 224. More particularly, thetracking system 222 determines a position and orientation (i.e., pose)of objects (e.g., surgical tool 234, femur 206) with respect to acoordinate frame of reference and tracks (i.e., continuously determines)the pose of the objects during a surgical procedure. According tovarious embodiments, the tracking system 222 may be any type ofnavigation system, including a non-mechanical tracking system (e.g., anoptical tracking system), a mechanical tracking system (e.g., trackingbased on measuring the relative angles of joints 236 of the robotic arm232), or any combination of non-mechanical and mechanical trackingsystems.

In the embodiment shown in FIG. 2, the tracking system 222 includes anoptical tracking system. Accordingly, tracking system 222 includes afirst fiducial tree 240 coupled to the tibia 208, a second fiducial tree241 coupled to the femur 206, a third fiducial tree 242 coupled to thebase 230, one or more fiducials 244 coupled to surgical tool 234, and adetection device 246 configured to detect the three-dimensional positionof fiducials (i.e., markers on fiducial trees 240-242). As shown in FIG.2, detection device 246 includes a pair of cameras 248 in a stereoscopicarrangement. The fiducial trees 240-242 include fiducials, which aremarkers configured to show up clearly to the cameras 248 and/or beeasily detectable by an image processing system using data from thecameras 248, for example by being highly reflective of infraredradiation (e.g., emitted by an element of tracking system 222). Thestereoscopic arrangement of the cameras 248 on detection device 246allows the position of each fiducial to be determined in 3D-spacethrough a triangulation approach. Each fiducial has a geometricrelationship to a corresponding object, such that tracking of thefiducials allows for the tracking of the object (e.g., tracking thesecond fiducial tree 241 allows the tracking system 222 to track thefemur 206), and the tracking system 222 may be configured to carry out aregistration process to determine or verify this geometric relationship.Unique arrangements of the fiducials in the fiducial trees 240-242(i.e., the fiducials in the first fiducial tree 240 are arranged in adifferent geometry than fiducials in the second fiducial tree 241)allows for distinguishing the fiducial trees, and therefore the objectsbeing tracked, from one another.

Using the tracking system 222 of FIG. 2 or some other approach tosurgical navigation and tracking, the surgical system 200 can determinethe position of the surgical tool 234 relative to a patient's anatomicalfeature, for example femur 206, as the surgical tool 234 is used to makea cut in or otherwise modify the anatomical feature.

The computing system 224 is configured to create a surgical plan,control the robotic device 220 in accordance with the surgical plan tomake one or more surgical cuts, receive data relating to the location ofthe surgical tool 234, determine the location and orientation of cutsmade by the surgical tool 234, alter the surgical plan based on thedeterminations to minimize the relative error between cuts, and controlthe robotic device in accordance with the updated surgical plan.Accordingly, the computing system 224 is communicably coupled to thetracking system 222 and the robotic device 220 to facilitate electroniccommunication between the robotic device 220, the tracking system 222,and the computing system 224. Further, the computing system 224 may beconnected to a network to receive information related to a patient'smedical history or other patient profile information, medical imaging,surgical plans, surgical procedures, and to perform various functionsrelated to performance of surgical procedures, for example by accessingan electronic health records system. Computing system 224 includesprocessing circuit 260 and input/output device 262.

The input/output device 262 is configured to receive user input anddisplay output as needed for the functions and processes describedherein. As shown in FIG. 2, input/output device 262 includes a display264 and a keyboard 266. The display 264 is configured to displaygraphical user interfaces generated by the processing circuit 260 thatinclude, for example, information about surgical plans, medical imaging,settings and other options for surgical system 200, status informationrelating to the tracking system 222 and the robotic device 220, andtracking visualizations based on data supplied by tracking system 222.The keyboard 266 is configured to receive user input to those graphicaluser interfaces to control one or more functions of the surgical system200.

The processing circuit 260 includes a processor and memory device. Theprocessor can be implemented as a general purpose processor, anapplication specific integrated circuit (ASIC), one or more fieldprogrammable gate arrays (FPGAs), a group of processing components, orother suitable electronic processing components. The memory device(e.g., memory, memory unit, storage device, etc.) is one or more devices(e.g., RAM, ROM, Flash memory, hard disk storage, etc.) for storing dataand/or computer code for completing or facilitating the variousprocesses and functions described in the present application. The memorydevice may be or include volatile memory or non-volatile memory. Thememory device may include database components, object code components,script components, or any other type of information structure forsupporting the various activities and information structures describedin the present application. According to an exemplary embodiment, thememory device is communicably connected to the processor via theprocessing circuit 260 and includes computer code for executing (e.g.,by the processing circuit 260 and/or processor) one or more processesdescribed herein.

More particularly, processing circuit 260 is configured to facilitatethe creation of a preoperative surgical plan prior to the surgicalprocedure. According to some embodiments, the preoperative surgical planis developed utilizing a three-dimensional representation of a patient'sanatomy, also referred to herein as a “virtual bone model.” A “virtualbone model” may include virtual representations of cartilage or othertissue in addition to bone. To obtain the virtual bone model, theprocessing circuit 260 receives imaging data of the patient's anatomy onwhich the surgical procedure is to be performed (e.g., femur 206). Theimaging data may be created using any suitable medical imaging techniqueto image the relevant anatomical feature, including computed tomography(CT), magnetic resonance imaging (MRI), and/or ultrasound. The imagingdata is then segmented (i.e., the regions in the imaging correspondingto different anatomical features are distinguished) to obtain thevirtual bone model. For example, MRI-based scan data of a knee issegmented to distinguish the femur from surrounding ligaments,cartilage, and other tissue to obtain a three-dimensional model of theimaged femur.

Alternatively, the virtual bone model may be obtained by selecting athree-dimensional model from a database or library of bone models. Inone embodiment, the user may use input/output device 262 to select anappropriate model. In another embodiment, the processing circuit 260 mayexecute stored instructions to select an appropriate model based onimages or other information provided about the patient. The selectedbone model(s) from the database can then be deformed based on specificpatient characteristics, creating a virtual bone model for use insurgical planning and implementation as described herein.

A preoperative surgical plan can then be created based on the virtualbone model. The surgical plan may be automatically generated by theprocessing circuit 260, input by a user via input/output device 262, orsome combination of the two (e.g., the processing circuit 260 limitssome features of user-created plans, generates a plan that a user canmodify, etc.).

The preoperative surgical plan includes the desired cuts, holes, orother modifications to a patient's anatomy to be made using the surgicalsystem 200. More particularly, for a total knee arthroscopy procedure asdescribed herein, the preoperative plan includes the cuts necessary toform distal surface 102, posterior chamfer surface 104, posteriorsurface 106, anterior surface 108, and anterior chamfer surface 110 inideal relative orientations and positions. The pre-planned positions andorientations of the surfaces 102-110 are based on the geometry of theprosthetic to be joined to the surfaces 102-110 during the surgicalprocedure and information about the patient. Accordingly, the processingcircuit 260 may receive, access, and/or store a model of the prostheticto facilitate the generation of surgical plans.

The processing circuit 260 is further configured to generate a controlobject for the robotic device 220 in accordance with the surgical plan.The control object may take various forms according to the various typesof possible robotic devices (e.g., haptic, autonomous, etc). Forexample, in some embodiments, the control object defines instructionsfor the robotic device to control the robotic device to move within thecontrol object (i.e., to autonomously make one or more cuts of thesurgical plan guided by feedback from the tracking system 222). In someembodiments, the control object includes a visualization of the surgicalplan and the robotic device on the display 264 to facilitate surgicalnavigation and help guide a surgeon to follow the surgical plan (e.g.,without active control or force feedback of the robotic device). Inembodiments where the robotic device 220 is a haptic device, the controlobject may be a haptic object as described in the following paragraphs.

In an embodiment where the robotic device 220 is a haptic device, theprocessing circuit 260 is further configured to generate one or morehaptic objects based on the preoperative surgical plan to assist thesurgeon during implementation of the surgical plan by enablingconstraint of the surgical tool 234 during the surgical procedure. Ahaptic object may be formed in one, two, or three dimensions. Forexample, a haptic object can be a line, a plane, or a three-dimensionalvolume. A haptic object may be curved with curved surfaces and/or haveflat surfaces, and can be any shape, for example a funnel shape. Hapticobjects can be created to represent a variety of desired outcomes formovement of the surgical tool 234 during the surgical procedure. One ormore of the boundaries of a three-dimensional haptic object mayrepresent one or more modifications, such as cuts, to be created on thesurface of a bone. A planar haptic object may represent a modification,such as a cut, to be created on the surface of a bone (e.g.,corresponding to the creation of surfaces 102-110).

In an embodiment where the robotic device 220 is a haptic device, theprocessing circuit 260 is further configured to generate a virtual toolrepresentation of the surgical tool 234. The virtual tool includes oneor more haptic interaction points (HIPs), which represent and areassociated with locations on the physical surgical tool 234. In anembodiment in which the surgical tool 234 is a spherical burr (e.g., asshown in FIG. 2), an HIP may represent the center of the spherical burr.If the surgical tool 234 is an irregular shape, for example as for asagittal saw, the virtual representation of the sagittal saw may includenumerous HIPs. Using multiple HIPs to generate haptic forces (e.g.positive force feedback or resistance to movement) on a surgical tool isdescribed in U.S. application Ser. No. 13/339,369, titled “System andMethod for Providing Substantially Stable Haptics,” filed Dec. 28, 2011,and hereby incorporated by reference herein in its entirety. In oneembodiment of the present invention, a virtual tool representing asagittal saw includes eleven HIPs. As used herein, references to an“HIP” are deemed to also include references to “one or more HIPs.” Asdescribed below, relationships between HIPs and haptic objects enablethe surgical system 200 to constrain the surgical tool 234.

Prior to performance of the surgical procedure, the patient's anatomy(e.g., femur 206) is registered to the virtual bone model of thepatient's anatomy by any known registration technique. One possibleregistration technique is point-based registration, as described in U.S.Pat. No. 8,010,180, titled “Haptic Guidance System and Method,” grantedAug. 30, 2011, and hereby incorporated by reference herein in itsentirety. Alternatively, registration may be accomplished by 2D/3Dregistration utilizing a hand-held radiographic imaging device, asdescribed in U.S. application Ser. No. 13/562,163, titled “RadiographicImaging Device,” filed Jul. 30, 2012, and hereby incorporated byreference herein in its entirety. Registration also includesregistration of the surgical tool 234 to a virtual tool representationof the surgical tool 234, so that the surgical system 200 can determineand monitor the pose of the surgical tool 234 relative to the patient(i.e., to femur 206). Registration of allows for accurate navigation,control, and/or force feedback during the surgical procedure.

The processing circuit 260 is configured to monitor the virtualpositions of the virtual tool representation, the virtual bone model,and the control object (e.g., virtual haptic objects) corresponding tothe real-world positions of the patient's bone (e.g., femur 206), thesurgical tool 234, and one or more lines, planes, or three-dimensionalspaces defined by forces created by robotic device 220. For example, ifthe patient's anatomy moves during the surgical procedure as tracked bythe tracking system 222, the processing circuit 260 correspondinglymoves the virtual bone model. The virtual bone model thereforecorresponds to, or is associated with, the patient's actual (i.e.physical) anatomy and the position and orientation of that anatomy inreal/physical space. Similarly, any haptic objects, control objects, orother planned automated robotic device motions created during surgicalplanning that are linked to cuts, modifications, etc. to be made to thatanatomy also move in correspondence with the patient's anatomy. In someembodiments, the surgical system 200 includes a clamp or brace tosubstantially immobilize the femur 206 to minimize the need to track andprocess motion of the femur 206.

For embodiments where the robotic device 220 is a haptic device, thesurgical system 200 is configured to constrain the surgical tool 234based on relationships between HIPs and haptic objects. That is, whenthe processing circuit 260 uses data supplied by tracking system 222 todetect that a user is manipulating the surgical tool 234 to bring a HIPin virtual contact with a haptic object, the processing circuit 260generates a control signal to the robotic arm 232 to provide hapticfeedback (e.g., a force, a vibration) to the user to communicate aconstraint on the movement of the surgical tool 234. In general, theterm “constrain,” as used herein, is used to describe a tendency torestrict movement. However, the form of constraint imposed on surgicaltool 234 depends on the form of the relevant haptic object. A hapticobject may be formed in any desirable shape or configuration. As notedabove, three exemplary embodiments include a line, plane, orthree-dimensional volume. In one embodiment, the surgical tool 234 isconstrained because a HIP of surgical tool 234 is restricted to movementalong a linear haptic object. In another embodiment, the haptic objectis a three-dimensional volume and the surgical tool 234 may beconstrained by substantially preventing movement of the HIP outside ofthe volume enclosed by the walls of the three-dimensional haptic object.In another embodiment, the surgical tool 234 is constrained because aplanar haptic object substantially prevents movement of the HIP outsideof the plane and outside of the boundaries of the planar haptic object.For example, the processing circuit 260 can establish a planar hapticobject corresponding to a planned planar distal cut needed to create adistal surface 102 on femur 206 in order to confine the surgical tool234 substantially to the plane needed to carry out the planned distalcut.

For embodiments where the robotic device 220 is an autonomous device,the surgical system 200 is configured to autonomously move and operatethe surgical tool 234 in accordance with the control object. Forexample, the control object may define areas relative to the femur 206for which a cut should be made. In such a case, one or more motors,actuators, and/or other mechanisms of the robotic arm 232 and thesurgical tool 234 are controllable to cause the surgical tool 234 tomove and operate as necessary within the control object to make aplanned cut, for example using tracking data from the tracking system222 to allow for closed-loop control.

The processing circuit 260 is further configured to record and store theinstantaneous position of a tool center point (TCP) of the surgical tool234 (e.g., the location of the virtual tool representation relative tothe virtual bone model) based on data provided by the tracking system222 as the surgical tool 234 carries out the preoperative surgical plan.As discussed in detail below with reference to FIGS. 3-10, theprocessing circuit 260 uses recorded TCP positions of the surgical tool234 to determine deviations from the surgical plan and updates thepreoperative surgical plan to intraoperatively update the surgical planto minimize the relative error between multiple cuts. In someembodiments, the tracking of the TCP may be of a higher accuracy orresolution than the haptic objects, a surgeon's perception or dexterity,and/or the tolerances of automated robotic movements such that errors incuts (i.e., deviations from planned cuts) that were made using thesurgical system 200 can be determined and quantified. As described infurther detail below with reference to FIGS. 3-10, the processingcircuit 260 is configured to use the recorded tool center pointpositions to determine the location and orientation of cuts made by thesurgical tool 234, compare these locations and orientations to thesurgical plan, and update the surgical plan for subsequent cuts tominimize the relative error between cuts.

Referring now FIG. 3, a flowchart showing a process 300 for minimizingrelative error in cuts made with a robotically-assisted surgical systemin a surgical procedure is shown, according to an exemplary embodiment.The process 300 can be carried out by the surgical system 200 shown inFIG. 2, for example as part of a total knee arthroplasty procedure.Accordingly, for the sake of clarity, reference is made to elements ofthe surgical system 200 in the following description.

At step 302, a surgical plan is established that includes multiplesurgical cuts to be carried out by a surgical tool. For example,processing circuit 260 may automatically generate a surgical plan basedon imaging data of a patient and/or other information related to thepatient and/or the procedure. In some embodiments, a surgeon or otheruser creates or modifies the surgical plan using input/output device 262of computing system 224.

At step 304, a registration process is carried out to register thepatient anatomy and surgical tool to align the planned cuts with thepatient's anatomy. For example, the registration process may be carriedout by the tracking system 222 in communication with the processingcircuit 260 to register a virtual bone model to a physical bone of thepatient (e.g., femur 206) and a HIP to the surgical tool 234. Asmentioned above, the registration process may be any suitableregistration process. The registration process includes determining thecoordinates of the physical bone, the preplanned cuts, and the surgicaltool within a Euclidean coordinate system used by the processing circuit260.

At step 306, a control object is created by the processing circuit 260to facilitate the surgical tool 234 in making the planned cutsconsistent with the surgical plan. For example, the planned cuts may bedefined by planes aligned with desired post-cut surfaces of a bone(e.g., surfaces 102-110 of FIG. 1), such that a control object (e.g., ahaptic object) includes a planar control object for each of the plannedcuts that substantially confines the surgical tool to move in the planenecessary to make the cut (e.g., in planes coplanar with surfaces102-110 of FIG. 1). In some embodiments, a haptic object is configuredto confine the surgical tool to complete the planned cuts in aparticular order, for example by confining the surgical tool to a firstplanar haptic object until the first cut is made, and then confining thesurgical tool to a second planar haptic object until the second cut ismade, and so on.

At step 308, the tool center point (TCP) of the surgical tool is trackedas the first cut is made (e.g., by a surgeon as confined by a hapticobject or autonomously by the robotic device 220). The TCP may betracked by the tracking system 222, for example based on a fiducial 244mounted on the surgical tool 234. The processing circuit 260 recordsinstantaneous positions of the TCP within a pre-defined Euclidean space.In some embodiments, the TCP is the central point of the distal end ofan end effector of the surgical tool 234, or has a known geometricrelationship with an effective end of the surgical tool 234 (i.e., thepoint on the tool that cuts, saws, files, grinds, etc. a bone), so thatthe TCP corresponds to a position of a modification to the patientanatomy made by the end effector. In some embodiments, the trackingsystem 222 and the computing system 224 track the tool center point witha higher accuracy or resolution than a surgeon can make a cut, than therobotic device 230 can move the surgical tool 234, and/or than a hapticboundary can confine the surgical tool, such that tracking the toolcenter point may be used to determine a deviation from a planned cut.

At step 310, the location and orientation of the cut and the deviationfrom the corresponding planned cut are determined. The location andorientation of the cut may be determined by the processing circuit 260by identifying tracked TCP positions that correspond to the cut andfitting a plane to the identified TCP positions. For example, TCPpositions may be continuously recorded as the surgical tool is movedinto position to make the cut, as a partial cuts are made, or as amulti-stage cut is made, such that the TCP positions corresponding tothe deepest or most impactful motions of the surgical tool (i.e., themovements that remove the most bone or a deepest layer of bone) areidentified by the processing circuit 260 as the TCP positions relevantto determining the location and orientation of the cut. In some cases,the relevant TCP positions are those which are positioned along asurface of a 3-D cloud of recorded TCP positions. The processing circuit260 then fits a plane (“recorded cut plane”) to the relevant TCPpositions (e.g., defining a surface of the 3-D cloud of recorded TCPpositions). The processing circuit 260 may use any three-dimensionaldata-fitting technique to fit the recorded cut plane to the recorded TCPpositions.

The processing circuit 260 then compares the recorded cut plane to theplanned cut to determine the deviation between the recorded cut plane(i.e., the real-world, actual cut) and the planned cut. The deviationmay include a translational deviation and/or a rotational deviation. Thetranslational deviation is determined by calculating the shortestdistance between the centroid of the planned cut to the recorded cutplane. The rotational deviation is determined by calculating the degreeto which the recorded cut plane is rotated about one or more axes (e.g.,of the Euclidean coordinate system, of the planned cut) relative toplanned cut.

At step 312, based on the calculated deviations, the processing circuit260 updates the surgical plan for the remaining planned cuts to minimizethe relative error between cuts. An embodiment of this process isdescribed in detail with respect to FIGS. 4-10. According to someembodiments, minimizing the relative error between cuts includespreserving an originally-planned overall shape formed by the plannedcuts to the greatest possible extent. Error minimization may also takeinto consideration the relative error in the position and orientation ofthe cuts relative to the patient's bone, other anatomical features,other surgical steps, or prosthetic components.

After the surgical plan is updated at step 312, the process returns tostep 306, where an updated control object is created (or modified from acontrol object formed previously) based on the updated surgical plan, asdescribed above. A second cut is made while the TCP is tracked at step308, as described above for the first cut. At step 310, the location andorientation of the second actual cut is determined, and the deviation ofthe second actual cut from the second planned cut (based on the updatedsurgical plan and/or the original surgical plan) is determined. Thesurgical plan is against updated based on the deviation at step 312, andthe process 300 may return again to step 306.

The process 300 thereby repeatedly loops through steps 306-312 as eachplanned cut is made. In some embodiments, the surgical plan is updatedfor every cut made as part of the surgical plan, while in otherembodiments the surgical plan is only updated after a portion of thecuts are made. For example, the surgical plan may be updated afteralternating cuts or after every third cut. As another example, thesurgical plan may be updated only if the deviations determined in step310 exceed a certain error threshold and/or fall below a certainthreshold.

Referring now to FIGS. 4-10, a process 400 for relative errorminimization in the femoral distal, posterior chamfer, posterior,anterior, and anterior chamfer cuts in a total knee arthroplastyprocedure is shown, according to an exemplary embodiment. FIG. 4 shows aflowchart depicting process 400, and FIGS. 5-10 are illustrations usefulfor explaining the process 400 shown in FIG. 4. Process 400 is anembodiment of process 300 of FIG. 3. As such, process 400 can also becarried out by surgical system 200 of FIG. 2, and, for the sake ofclarity, reference is made to components of surgical system 200 in thefollowing description of process 400.

At step 402, a surgical plan is established for the five femoral cuts ofa total knee arthroplasty procedure, namely the distal, posteriorchamfer, posterior, anterior, and anterior chamfer cuts. According tovarious embodiments, the surgical plan is automatically generated byprocessing circuit 260 based on medical imaging data and other patientor procedure related information, input to computing system 224 by asurgeon or other user, imported from an external computing system by thecomputing system 224 via a network, or some combination of those orother planning procedures.

The surgical plan includes a planned cut for each of the five cuts, ingeneral aimed at modifying a femur (e.g., femur 206) to create surfacescorresponding to distal surface 102, posterior chamfer surface 104,posterior surface 106, anterior surface 108, and anterior chamfersurface 110 of femur 100 shown in FIG. 1. Although various motions ofthe surgical tool 234 may be required to carry out the planned cutsdescribed herein, the planned cuts and subsequent planned cuts describedbelow are represented by the desired planar surfaces of the femur to becreated by the corresponding cuts. Accordingly, each planned cutincludes a centroid that defines a central point of the planned cut in athree-dimensional reference Euclidean coordinate system (i.e., to fix alocation of the planned cut) and an angular rotation of the planned cutrelative to a reference plane around the axes of a Euclidean coordinatesystem (i.e., an angle relative to the x-axis, y-axis, and/or z-axis tofix an orientation of the planned cut relative to the other plannedcuts), as illustrated in FIGS. 5A-5C.

FIGS. 5A-5C show planned cuts 500, namely distal cut 502, posteriorchamfer cut 504, posterior cut 506, anterior cut 508, and anteriorchamfer cut 510, aligned on a Euclidean coordinate system defined byaxes 512. As shown, each cut 502-510 has a position that can be definedby a centroid of the cut, and a relative orientation that can be definedbased on rotation about one or more axes 512. For example, in FIG. 5A, aprojection 514 of the y-axis 516 on the distal cut 502 shows that thedistal cut 502 can be rotated around the y-axis (illustrated by rotationindicator 517). FIG. 5B shows a projection 518 of the z-axis 520 on theposterior cut 506 that shows that the posterior cut 506 can be rotatedaround the z-axis (illustrated by rotation indicator 521), while FIG. 5Cshows a projection 522 of the x-axis 524 on the posterior cut 506 thatshows that the posterior cut 506 can be rotated around the x-axis(illustrated by rotation indicator 525). In some embodiments, theplanned distal cut 502 is taken as reference planar cut with an originat its centroid, and the other planned cuts are defined based on athree-dimensional location of a centroid relative to the centroid of thedistal cut 502 and the rotations about the axes 516, 520, 524 of thereference coordinate system needed to rotate the distal cut 502 to matchthe orientation of the other planned cut. As discussed in detail below,errors in the cuts can also be characterized based on rotational errorsabout the axes 516, 520, 524 and deviations from the locations of thecentroids of the planned cuts 502-510.

The planned cuts 502-510 of the surgical plan established at step 402 ofprocess 400 are shown in FIG. 6 in a cross-sectional view, and referredto collectively in the following as the “original surgical plan” 600.Although each cut 502-510, as described above, is a planar object inthree-dimensional space, two-dimensional cross-sectional views are shownin FIGS. 6-10 for clarity and to ease explanation of process 400.

At step 404, the processing circuit 260 generates a control object basedon the original surgical plan to facilitate the planned cuts. Accordingto some embodiments, the control object is a haptic object that includesa planar haptic object for each of the planned cuts 502-510, such thatthe haptic object is configured to confine the surgical tool 234substantially to the plane needed to make the corresponding cut. In someembodiments, a haptic object generated at step 404 confines the surgicaltool 234 substantially to the plane corresponding to the distal cut 502,such that the surgeon must make the distal cut before other cuts. Thecontrol object may have any form that controls or otherwise facilitatesthe surgical tool 234 of robotic device 220 to making the planned cuts.

At step 406, the surgical system 200 facilitates the distal cut whiletracking the tool center point (TCP) of the surgical tool 234. Accordingto some embodiments, step 406 includes a registration step to registerthe planned cuts 502-510 and the corresponding control object to thepatient's real-world anatomy (i.e., femur 206), as well as register thesurgical tool 234 to the same coordinate system, for example asdescribed in reference to step 304 of FIG. 3. The TCP can then bytracked by tracking system 222, with TCP positions determinable relativeto the planned cuts 502-510 and the patient's femur 206. In embodimentsinvolving a haptic object, one or more HIPS of the surgical tool 234 canalso be tracked by the tracking system 222 and processing circuit 260relative to the haptic object in order to generate controls signals tothe robotic arm 232 to confine the surgical tool 234 to a haptic object.In other embodiments, the robotic arm 232 and the surgical tool 234autonomously make the posterior chamfer cut in coordination with thetracking system 222 as controlled by the processing circuit 260. Thesurgical tool 234 can thus be used, for example autonomously or by asurgeon as confined to a haptic object, to make the distal cut 502 infemur 206 while the tracking system 222 tracks instantaneous TCPpositions in the registered, three-dimensional Euclidean coordinatesystem of the planned cuts (e.g., as shown in FIGS. 5A-5C).

At step 408, the recorded distal cut plane 700 is determined by theprocessing circuit 260. The recorded distal cut plane 700 is illustratedin FIG. 7. To determine the recorded distal cut plane 700, theprocessing system identifies the recorded TCP positions that correspondto the cut made in femur 206 and fits a plane to those points. The TCPpositions that correspond to the cut made in femur 206 may be identifiedas those points that penetrate a virtual bone model of the femur 206 tothe greatest extent, that make up a boundary of a 3-D cloud of recordedTCP positions and that corresponds to the planned distal cut 502, andany other point identification approach. A plane may be fit to thosepositions (i.e., points defined in three-dimensions in the coordinatesystem of FIGS. 5A-5C) by some suitable plane fitting approach. Astatistical approach to fitting a plane to many points (e.g., more thanthree) may provide an accurate determination of the actual cut made bythe surgical tool 234 and characterized as the recorded distal cut plane700, even where all identified points do not lie in the fit plane. Therecorded distal cut plane 700 is thus determined, such that it can bedefined in a similar way as the distal cut 502 described with referenceto FIG. 5A.

At step 410, the processing system determines the error of the recordeddistal cut plane 700 relative to the planned distal cut 502 as in theoriginal surgical plan 600. As shown in FIG. 7A, the recorded distal cutplane 700 deviates from the planned distal cut 502 translationally(i.e., the recorded distal cut plane 700 is ‘lower’ than the planneddistal cut 502 in the cross-sectional view of FIG. 7) and rotationally(i.e., the recorded distal cut plane 700 is not parallel to the planneddistal cut 502). While shown as rotational error in the sagittal planefor the sake of visibility in the cross-section of FIG. 7A, therotational error of the recorded distal cut plane 700 considered at step410 is a rotation around the y-axis 516 as indicated in FIG. 5A (i.e., avarus/valgus angular error). While the recorded distal cut plane 700 mayalso have rotational errors about the x-axis 524 and z-axis 520, at step410 the varus/valgus angular error of the recorded distal cut plane 700is considered because of the way that a femoral prosthesis interactswith the femur 206 during trialing/implantation. When the prosthesis isplaced, the anterior surface 108 and posterior surface 106 substantiallyrestrict anterior-posterior translation in the y-direction,internal/external rotation about the z-axis 516, and flexion/extensionrotation about the x-axis 524. The distal surface 102 is left tocontribute errors in superior-inferior translation (in the z-direction)and in varus/valgus rotation. Thus, errors in superior-inferiortranslation and in varus/vulgus rotation are considered at step 410while other errors are considered in subsequent steps.

To account for these errors, two error terms are calculated in step 410,namely D_(distal) and A_(y_distal). D_(distal) is calculated as theshortest distance between the centroid of the distal cut 502 and therecorded distal cut plane 700. D_(distal) may also include a directionalcomponent (i.e., defined as a vector), or may be measured/defined in apredetermined direction (e.g., along the z-direction, normal to theplanned distal cut 502). A_(y_distal) is calculated as the angle ofrotation around the y-axis 516 from the planned distal cut 502 to therecorded distal cut plane 700.

At step 412, the planned posterior chamfer cut 504, posterior cut 506,anterior cut 508, and anterior chamfer cut 510 as in original surgicalplan 600 are adjusted based on the calculated error terms to generatefirst updated surgical plan 710 shown in FIG. 7B. The centroids of thefour remaining cuts 504-510 are each translated by D_(distal) along thedirection of error (e.g., along the z-direction), and the cuts 504-510are rotated by A_(y_distal). This adjustment takes the relative errorbetween the recorded distal cut plane 700 and the remaining cuts 504-510to zero along the z-direction (superior-inferior translation) and aroundthe y-axis 516 (varus/vulgus rotation), and results in the first updatedsurgical plan 710 shown in FIG. 7B. In some cases, an error in rotationabout the x-axis 724 between the recorded distal cut plane 700 and theremaining cuts 504-510 is still present, and is minimized in subsequentsteps.

At step 414, the control object is updated based on the adjusted plannedcuts 504-510 of first updated surgical plan 710. For example, in anembodiment where the haptic object includes a planar haptic object foreach of the planned cuts 502-510, such that the haptic object isconfigured to confine the surgical tool 234 substantially to the planeneeded to make the corresponding cut, the planar haptic objectcorresponding to each remaining cut is adjusted to confine the surgicaltool 234 substantially to the plane needed to make the adjusted cut inaccordance with the first updated surgical plan 710. In someembodiments, to save computational resources, only the control objectcorresponding to the next planned cut (i.e., according to the sequenceof cuts as in process 400) or the next two planned cuts is updated atstep 414 (i.e., the posterior chamfer cut and the posterior cut).

At step 416, the surgical system 200 facilitates the posterior chamfercut according to the first updated surgical plan 710. In someembodiments, the surgical tool 234, confined within a haptic object byrobotic arm 232 as controlled by the processing circuit 260 based ontracking information from the tracking system 222, is manipulated by asurgeon to make the posterior chamfer cut 504 as in first updatedsurgical plan 710. In other embodiments, the robotic arm 232 and thesurgical tool 234 autonomously make the posterior chamfer cut incoordination with the tracking system 222 and the processing circuit260. According to the embodiment of process 400 shown in FIG. 4, the TCPpositions need not by tracked in step 416, as the error determinationand adjustments steps are not carried out for the posterior chamfercuts. Skipping these steps (e.g.,) for the posterior chamfer cut maysave computation resources and avoid delays caused by computation times,without compromising the overall error minimization process. In otherembodiments, the TCP tracking, error determination, and plan updatingsteps (e.g., steps 308-312 of process 300) are carried out for each ofthe first four of the five femoral cuts or for all planned cuts.

At step 418, the surgical system 200 facilitates the posterior cut whiletracking the tool center point (TCP) of the surgical tool 234. Similarto step 406 described above, in step 418 surgical tool 234 can beautonomously controlled or manipulated by a surgeon confined by a hapticobject to make the updated posterior cut 506 in femur 206 while thetracking system 222 tracks instantaneous TCP positions in theregistered, three-dimensional Euclidean coordinate system of the plannedcuts (e.g., as shown in FIGS. 5A-5B).

At step 420, the processing circuit 260 uses the recorded TCP positionsto determine a recorded posterior cut plane. The recorded posterior cutplane 800 is illustrated in FIG. 8. As in step 408, and described inmore detail in reference thereto, to determine the recorded posteriorcut plane 800, the processing system identifies the recorded TCPpositions that correspond to the cut made in femur 206 and fits a planeto those points.

At step 422, the processing system determines the error of the recordedposterior cut plane 800 relative to the planned posterior cut 506 as infirst updated surgical plan 710. As shown in FIG. 8A, the recordedposterior cut plane 800 deviates from the updated planned posterior cut506 translationally (i.e., the recorded posterior cut plane 800 is tothe right of the updated planned posterior cut 506 in thecross-sectional view of FIG. 8A) and rotationally (i.e., the recordedposterior cut plane 800 is not parallel to the planned posterior cut506). The rotational deviation of the recorded posterior cut plane 800has two components: a rotation around the z-axis 520 (internal/externalangular error) as illustrated in FIG. 5B and a rotation around thex-axis 524 (flexion/extension angular error) as illustrated in FIG. 5C.Three error components are therefore determined for the recordedposterior cut plane 800, namely D_(posterior), A_(x_posterior), andA_(z_posterior). D_(posterior) is calculated as the shortest distancefrom the centroid of the planned posterior cut 506 to the recordedposterior cut plane 800. A_(x_posterior) is calculated as the angle ofrotation around the x-axis 524 from the planned posterior cut 506 to therecorded posterior cut plane 800. A_(z_posterior) is calculated as theangle of rotation around the z-axis 520 from the planned posterior cut506 to the recorded posterior cut plane 800.

At step 424, the processing circuit 260 adjusts the first updatedsurgical plan 710 (i.e., for the anterior cut and the anterior chamfercuts) based on the calculated error components of the recorded posteriorcut plane 800 to get second updated surgical plan 810 shown in FIG. 8B.Modifications based on D_(posterior), A_(x_posterior), andA_(z_posterior) are weighted based on a weighted parameter w, to resultin a reduction in of cutting error in the posterior cut of (w*100) %.The parameter w may be determined from experimental results or someother approach to determining an optimal value of w. For example, w maybe a number between zero and 1. To get from the first updated surgicalplan 710 to the second updated surgical plan 810, the location of theremaining cuts (i.e., anterior cut 508 and anterior chamfer cut 510) aretranslated by w*D_(posterior), and the planned cuts 508-510 are rotatedaround the x-axis by w*A_(z_postetior) and around the z-axis byw*A_(z_posterior) (in the directions of error minimization, i.e., thesame directions that posterior cut 506 would have to betranslated/rotated to align with recorded posterior cut plane 800).

At step 426, the control object is updated to correspond to the secondupdated surgical plan 810. As for step 414, in an embodiment where thecontrol object is a haptic object that includes a planar haptic objectfor each of the planned cuts 502-510, such that the haptic object isconfigured to confine the surgical tool 234 substantially to the planeneeded to make the corresponding cut, the planar haptic objectcorresponding to each remaining cut is adjusted to confine the surgicaltool 234 substantially to the plane needed to make the adjusted cut inaccordance with the second updated surgical plan 810. In someembodiments, each remaining cut (i.e., the anterior and anterior chamfercuts) may have a corresponding planar control object that is adjusted byw*D_(posterior), w*A_(x_posterior), and w*A_(z_posterior).

At step 428, the surgical system 200 facilitates the anterior cut whiletracking TCP positions. Similar to steps 406 and 418 described above, instep 428 surgical tool 234 can be autonomously controlled or manipulatedby a surgeon confined by a haptic object to substantially follow thesecond updated surgical plan 810 to make the updated planned anteriorcut 508 in femur 206 while the tracking system 222 tracks instantaneousTCP positions in the registered, three-dimensional Euclidean coordinatesystem of the planned cuts (e.g., as shown in FIGS. 5A-5B).

At step 430, the processing system determines the recorded anterior cutplane 900. The recorded anterior cut plane 900 is illustrated in FIG.9A. As in step 408, and described in more detail in reference thereto,to determine the recorded anterior cut plane 900, the processing systemidentifies the recorded TCP positions that correspond to the cut made infemur 206 and fits a plane to those points.

At step 432, the processing circuit 260 determines the error of therecorded anterior cut plane 900 relative to the updated planned anteriorcut 508 of second updated surgical plan 810. As shown in FIG. 9A, therecorded anterior cut plane 900 deviates from the updated plannedanterior cut 508 translationally (i.e., the recorded anterior cut plane900 is to the left of the updated planned anterior cut 508 in thecross-sectional view of FIG. 9) and rotationally (i.e., the recordedanterior cut plane 900 is not parallel to the planned anterior cut 508).The rotational deviation of the recorded anterior cut plane 900 has twocomponents: a rotation around the z-axis 520 (internal/external angularerror) as illustrated in FIG. 5B and a rotation around the x-axis 524(flexion/extension angular error) as illustrated in FIG. 5C. Three errorcomponents are therefore determined for the recorded anterior cut plane900, namely D_(anterior), A_(x_anterior), and A_(z_anterior).D_(anterior) is calculated as the shortest distance from the centroid ofthe planned anterior cut 508 to the recorded anterior cut plane 900.A_(x_anterior) is calculated as the angle of rotation around the x-axis524 from the updated planned anterior cut 508 to the recorded anteriorcut plane 900. A_(z_anterior) is calculated as the angle of rotationaround the z-axis 520 from the updated planned anterior cut 508 to therecorded anterior cut plane 900.

At step 434, the processing circuit 260 adjusts the surgical plan forthe anterior chamfer cut 510 based on the calculated error components ofthe recorded anterior cut plane 900 to get third updated surgical plan910 shown in FIG. 9B. To obtain third updated surgical plan 910, theupdated planned anterior chamfer cut 510 of second updated surgical plan810 is translated by (1−w)*D_(anterior), rotated around the x-axis by(1−w)*A_(x_anterior) and rotated around the z-axis by(1−w)*A_(z_anterior) (in the directions of error minimization, i.e., thesame directions that planned anterior cut 510 as in second updatedsurgical plan 810 would have to be translated/rotated to align withrecorded anterior cut plane 900). An updated plan for the anteriorchamfer cut 510 is thereby obtained.

At step 436, the processing circuit 260 updates the control object basedon the third updated surgical plan 910. For example, in someembodiments, a planar haptic object corresponding to the anteriorchamfer cut 510 is adjusted by (1−w)*D_(anterior), (1−w)*A_(x_anterior),and (1−w)*A_(z_anterior). The processing circuit 260 thereby generates acontrol object suitable for facilitating the anterior chamfer cut 510according to third updated surgical plan 910.

At step 438, the surgical system 200 facilitates the anterior chamfercut to carry out third updated surgical plan 910. Similar to step 416described above, in step 428 surgical tool 234 can be autonomouslycontrolled or manipulated by a surgeon confined by a haptic object tomake the anterior chamfer cut 510 in femur 206. In some embodiments, theTCP positions of the surgical tool 234 are tracked while the anteriorchamfer cut is made for the sake of overall error assessment and/orother medical purposes. FIG. 10 shows the final completed cuts 1000relative to the original surgical plan 600. As shown, the relative errorbetween the cuts has been lessened by the intraoperative assessment andplan updates, for example by shifting the anterior cut towards theposterior cut and rotating it to better preserve the originally-plannedoverall shape of the cuts. In this way, intraoperative updates to theplan and adjustments as described herein can contribute to the overallsuccess of the arthroplasty procedure.

The construction and arrangement of the systems and methods as shown inthe various exemplary embodiments are illustrative only. Although only afew embodiments have been described in detail in this disclosure, manymodifications are possible (e.g., variations in sizes, dimensions,structures, shapes and proportions of the various elements, values ofparameters, use of materials, colors, orientations, etc.). For example,the position of elements may be reversed or otherwise varied and thenature or number of discrete elements or positions may be altered orvaried. Accordingly, all such modifications are intended to be includedwithin the scope of the present disclosure. The order or sequence of anyprocess or method steps may be varied or re-sequenced according toalternative embodiments. Other substitutions, modifications, changes,and omissions may be made in the design, operating conditions andarrangement of the exemplary embodiments without departing from thescope of the present disclosure.

What is claimed is:
 1. A surgical system, comprising: a robotic devicehaving a surgical tool configured to modify a bone; a tracking systemconfigured to provide tracking data corresponding to a location of thesurgical tool; and a processing system communicably coupled to therobotic device and configured to: store a surgical plan comprising afirst planned cut and one or more additional planned cuts, eachadditional cut defined by a relative angle and distance from the firstplanned cut; receive first tracking data from the tracking system whilethe surgical tool makes a cut substantially corresponding to the firstplanned cut; determine a recorded first cut plane based on the firsttracking data; determine an error between the recorded first cut planeand the planned first cut, the error comprising a deviation from theplanned first cut, wherein the deviation is at least one of atranslational deviation or a rotational deviation; update the surgicalplan by modifying the one or more additional planned cuts based on thedeviation.
 2. The surgical system of claim 1, wherein the bone is afemur, and wherein the first planned cut is a distal cut, and whereinthe one or more additional planned cuts comprise a planned posteriorchamfer cut, a planned posterior cut, a planned anterior cut, and aplanned anterior chamfer cut.
 3. The surgical system of claim 1, theprocessing system further configured to: receive second tracking datafrom the tracking system while the surgical tool makes a second cutsubstantially corresponding to a second planned cut; determine arecorded second cut plane based on the second tracking data; determine asecond error between the recorded second cut plane and the plannedsecond cut, the second error comprising a second deviation, wherein thesecond deviation comprises at least one of a second translationaldeviation and a second rotational deviation; update the surgical plan bymodifying the additional planned cuts based on the second deviation anda weighting parameter.
 4. The surgical system of claim 3, wherein thesecond deviation comprises a translational deviation, a first rotationaldeviation about a first axis, and a second rotational deviation about asecond axis.
 5. The surgical system of claim 1, the processing systemfurther configured to generate a control object corresponding to thesurgical plan, the robotic device configured to control the surgicaltool in accordance with the control object.
 6. The surgical system ofclaim 5, the robotic device further comprising a robotic arm, therobotic arm configured to: allow a user to manipulate the surgical tool;and provide force feedback to the user when the surgical tool meets aboundary of the control object.
 7. The surgical system claim 5, whereinthe surgical system is further configured to update the control objectbased on the deviation.
 8. A method for minimizing relative cuttingerror in a total knee arthroscopy procedure, comprising: establishing asurgical plan comprising a planned distal cut, a planned posteriorchamfer cut, a planned posterior cut, a planned anterior cut, and aplanned anterior chamfer cut; generating a control object correspondingto the surgical plan; controlling, with a robotic device, a surgicaltool based on the control object; cutting a femur with the surgical toolto substantially carry out the planned distal cut while recording distaltracking data corresponding to a position of the surgical tool;determining, based on the distal tracking data, an error between arecorded distal cut and the planned distal cut, the error defined byD_(distal) and A_(y_distal), wherein D_(distal) is determined by adistance between the planned distal cut and the recorded distal cut andA_(y_distal) is determined by a first angular rotation from the planneddistal cut to the recorded distal cut about a first axis; updating thesurgical plan by modifying the planned posterior chamfer cut, theplanned posterior chamfer cut, the planned anterior cut, and the plannedanterior chamfer cut by D_(distal) and A_(y_distal) to get a firstupdated surgical plan; and updating the control object based on thefirst updated surgical plan.
 9. The method of claim 8, furthercomprising: cutting the femur with the surgical tool to substantiallycarry out the planned posterior chamfer cut; cutting the femur with thesurgical tool to substantially carry out the planned posterior cut whilerecording posterior tracking data corresponding to the position of thesurgical tool; determining, based on the posterior tracking data, aposterior error between a recorded posterior cut and the plannedposterior cut, the posterior error defined by D_(posterior),A_(x_posterior), and A_(z_osterior), wherein D_(posterior) is determinedby a posterior distance between the planned posterior cut and therecorded posterior cut, A_(x_posterior) is determined by a secondangular rotation from the planned posterior cut to the recordedposterior cut about a second axis, and A_(z_posterior) is determined bya third angular rotation from the planned posterior cut to the recordedposterior cut about a third axis; updating the first updated surgicalplan by modifying the planned anterior cut and the planned anteriorchamfer cut by w*D_(posterior), w*A_(x_posterior), andw*A_(x_posterior), to get a second updated surgical plan, wherein w is aweighting parameter; and updating the control object based on the secondupdated surgical plan.
 10. The method of claim 9, further comprising:cutting the femur with the surgical tool to substantially carry out theplanned anterior cut while recording anterior tracking datacorresponding to the position of the surgical tool; determining, basedon the anterior tracking data, an anterior error between a recordedanterior cut and the planned anterior cut, the anterior error defined byD_(anterior), A_(x_anterior), and A_(z_anterior), wherein D_(anterior)is determined by an anterior distance between the planned anterior cutand the recorded anterior cut, A_(x_anterior) is determined by a fourthangular rotation from the planned anterior cut to the recorded anteriorcut about the second axis, and A_(z_anterior) is determined by a fifthangular rotation from the planned anterior cut to the recorded anteriorcut about the third axis; updating the second updated surgical plan bymodifying the planned anterior chamfer cut by (1−w)*D_(posterior),(1−w)*A_(x_anterior), and (1−w)*A_(y_anterior), to get a third updatedsurgical plan; and updating the control object based on the thirdupdated surgical plan.
 11. The method of claim 10, further comprisingcutting the femur to substantially carry out the planned anteriorchamfer cut according to the third updated surgical plan.
 12. The methodof claim 10, wherein w is chosen to minimize a relative error of acombined resultant cut shape compared to a combined planned cut shapecorresponding to the planned distal cut, the planned posterior chamfercut, the planned posterior cut, the planned anterior cut, and theplanned anterior chamfer cut.
 13. The method of claim 8, whereincontrolling, with a robotic device, a surgical tool based on the controlobject comprises: tracking, with a tracking system, a haptic interactionpoint corresponding to the surgical tool; detecting, in a processingsystem, when the haptic interaction point reaches a boundary of thecontrol object; and generating, in response to detecting that the hapticinteraction point reaches the boundary of the control object, a controlsignal to the robotic device to provide force feedback to a user. 14.The method of claim 8, wherein the surgical tool is at least one of aspherical burr and a sagittal saw.
 15. A robotic device, comprising: abase; a robotic arm mounted on the base; a surgical tool mounted on therobotic arm and comprising an end effector configured to modify a bone;the robotic arm controlled by a processing system in accordance with acontrol object generated by the processing system, the processing systemconfigured to: establish a surgical plan comprising a planned distalcut, a planned posterior chamfer cut, a planned posterior cut, a plannedanterior cut, and a planned anterior chamfer cut; create the controlobject based on the surgical plan; track a tool center point of thesurgical tool while the end effector is used to substantially carry outthe planned distal cut to generate distal tracking data; determine,based on the distal tracking data, an error between a recorded distalcut and the planned distal cut, the error defined by at least one of adistance between the planned distal cut and the recorded distal cut anda first angular rotation from the planned distal cut to the recordeddistal cut about a first axis; update the surgical plan by modifying theplanned posterior chamfer cut, the planned posterior chamfer cut, theplanned anterior cut, and the planned anterior chamfer cut based on theerror to get a first updated surgical plan; and update the controlobject based on the first updated surgical plan.
 16. The robotic deviceof claim 15, the processing system further configured to: recordposterior tracking data corresponding to a tool center point of thesurgical tool while the end effector is used to substantially carry outthe planned posterior cut; determine, based on the posterior trackingdata, a posterior error between a recorded posterior cut and the plannedposterior cut, the posterior error defined by a posterior distancebetween the planned posterior cut and the recorded posterior cut, asecond angular rotation from the planned posterior cut to the recordedposterior cut about a second axis, and a third angular rotation from theplanned posterior cut to the recorded posterior cut about a third axis;update the first updated surgical plan by modifying the planned anteriorcut and the planned anterior chamfer cut based on the posterior errorand a weighting parameter to get a second updated surgical plan; andupdate the control object based on the second updated surgical plan. 17.The robotic device of claim 16, the processing system further configuredto: record anterior tracking data corresponding to a tool center pointof the surgical tool while the end effector is used to substantiallycarry out the planned anterior cut; determine, based on the anteriortracking data, an anterior error between a recorded anterior cut and theplanned anterior cut, the anterior error defined by an anterior distancebetween the planned anterior cut and the recorded anterior cut, a fourthangular rotation from the planned anterior cut to the recorded anteriorcut about the second axis, and a fifth angular rotation from the plannedanterior cut to the recorded anterior cut about the third axis; updatethe second updated surgical plan by modifying the planned anteriorchamfer cut based on the anterior error and a second weighting parameterto get a third updated surgical plan; and update the control objectbased on the third updated surgical plan.
 18. The control device ofclaim 15, the surgical tool further comprising a fiducial, the fiducialconfigured to be tracked by a tracking system to provide position datato the processing system.
 19. The control device of claim 15, whereinthe robotic arm is controlled by the processing system in accordancewith the control object to autonomously move the end effector to carryout the planned distal cut.
 20. The control device of claim 15, whereinthe robotic arm is controlled by the processing system in accordancewith the control object by providing force feedback; and wherein: theforce feedback is based on an interaction between a virtual hapticinteraction point and a virtual haptic object; the virtual hapticinteraction point corresponds to a tracked position of the end effector;and the force feedback comprises a force that substantially prevents auser from moving the haptic interaction point through a boundary of thevirtual haptic object.